First Alert Weather Academy: Sunset colors

SAVANNAH, Ga. (WTOC) - Have you or your children ever wondered why the sky is blue? Or why the sun is a different color at sunset?

When a beam of sunlight strikes a molecule in the atmosphere, what’s called “scattering” occurs, sending some of the light’s wavelengths off in different directions. This happens millions of times before that beam gets to your eyeball at sunset.

The two main molecules in air, oxygen and nitrogen, are very small compared to the wavelengths of the incoming sunlight—about a thousand times smaller. That means that they preferentially scatter the shortest wavelengths, which are the blues and purples.

Basically, that's why the daytime sky is blue. The daytime sky would actually look purple to humans were it not for the fact that the sensitivity of our eyes peaks in the middle part of the spectrum—that is, closer to blue than to purple.

But at sunset, the light takes a much longer path through the atmosphere to your eye than it did at noon, when the sun was right overhead. And that is enough to make a big difference as far as our human eyes are concerned. It means that much of the blue has scattered out long before the light reaches us, leaving a disproportionate amount of oranges and reds as that beam of light hits the East Coast.